DataSet Update Command Error

I have a dataset that I want to use an update command to update the
underlying table. I have fields that are not mandatory. I'm getting an
error when there is no data in any one of the textboxes. What do I need to
do differently to accomodate empty textboxes?

Here's a code snippet:
Dim iRIN As Integer = CType(e.Item.FindControl("txtRIN"), TextBox).Text
Dim sDiv As String = CType(e.Item.FindControl("txtDivision"), TextBox).Text
Dim sCall As String = CType(e.Item.FindControl("txtCall"), TextBox).Text
Dim sDistrict As String = CType(e.Item.FindControl("txtDistrict"),
TextBox).Text
Dim sAssignment As String = CType(e.Item.FindControl("txtAssignment"),
TextBox).Text
Dim sSerial As String = CType(e.Item.FindControl("txtSerial"), TextBox).Text
Dim sTG As String = CType(e.Item.FindControl("txtTalkgrp"), TextBox).Text
Dim sModel As String = CType(e.Item.FindControl("txtModel"), TextBox).Text
Dim bMike As Boolean = CType(e.Item.FindControl("txtMike"), TextBox).Text
Dim bCharger As Boolean = CType(e.Item.FindControl("txtCharger"),
TextBox).Text
Dim iChargerNo As String = CType(e.Item.FindControl("txtChargerNo"),
TextBox).Text
Dim sOwner As String = CType(e.Item.FindControl("txtOwner"), TextBox).Text
Dim dRepair As String = CType(e.Item.FindControl("txtRepair"), TextBox).Text
Dim iScanNo As Integer = CType(e.Item.FindControl("txtScanNo"),
TextBox).Text
Dim sRemarks As String = CType(e.Item.FindControl("txtRemarks"),
TextBox).Text
Dim sCount As String = CType(e.Item.FindControl("txtCount"), TextBox).Text
Dim key As Integer = DataList1.DataKeys(e.Item.ItemIndex)

Dim strSQL As String = "UPDATE Radios SET Count = '" & sCount & "',
strSerialNumber = '" & sSerial & "' , strCall = '" & sCall & "'"
strSQL = strSQL & ", intRIN6Digit = " & iRIN & ", strModel = '" & sModel &
"', strAssignment = '" & sAssignment & "'"
strSQL = strSQL & ", strDistrict-Section = '" & sDistrict & "', strTalkGroup
= '" & sTG & "', intAssetTagNo = " & iScanNo & ""
strSQL = strSQL & ", dtSentForRepair = #" & dRepair & "#, strRemarks = '" &
sRemarks & "', strDivision = '" & sDiv & "'"
strSQL = strSQL & ", bIndividualCharger = " & bCharger & ", bP-S_Mike = " &
bMike & ", strOwner = '" & sOwner & "', intChargerNumber = " & iChargerNo &
"WHERE intRIN6Digit = " & key & ""

Try
Dim cmd As New OleDbCommand(strSQL, cnn)
cnn.Open()
Dim objDataReader As OleDbDataReader
objDataReader = cmd.ExecuteReader()
DataList1.DataSource = objDataReader
FillDataList()



Thanks much!!
Lynnette